In order to be able to actuate a valve member, which with an exhaust gas recirculation valve is used for controlling an exhaust gas recirculation rate, an actuating drive is required. Increased requirements are made on an actuating drive of this type. For example soot carried along in the exhaust gas can result in that the valve member sticks to a valve seat complementary thereto, as a result of which relatively high driving forces are required in order to be able to lift the valve member off the seat. In addition, the valve member must be able to realise a comparatively large stroke to achieve high exhaust gas recirculation rates. Furthermore, comparatively short actuating times have to be realised. Similar problems can also occur with other components of exhaust systems. For example with an exhaust gas turbocharger. Such an exhaust gas turbocharger can be equipped with a so-called wastegate valve with which with a turbine of the exhaust gas turbocharger the high-pressure side can be connected with the low-pressure side, for example in order to avoid overloading the turbocharger. Since the wastegate valve is also located on the exhaust gas side, it also requires relatively large actuating forces for opening, for closing and for keeping it closed. In addition there are turbochargers with adjustable guide blade geometry in order to adapt the turbocharger to different operating states of the internal combustion engine equipped with said turbocharger. Here, too, bi-directionally operating actuating drives can be employed.
From DE 10 2005 028 372 an actuating drive is known wherein an electric motor rotationally drives an actuating shaft via a gearing. For realising a large gear ratio and thus a large rotational moment on the actuating shaft two first gears with the same number of teeth are connected in a rotationally fixed manner with a driveshaft of the electric motor and thereby arranged so that their teeth are offset from each other. The two first gears mesh with two second gears which likewise have the same number of teeth and are arranged with tooth offset axially next to each other.
From DE 198 54 614 A1 an actuating device is known, wherein an actuating force amplifier is integrated in a bidirectionally adjustable actuator. The actuator consists of two rods which on the one hand are coupled together via a compression spring and on the other hand via the actuating force amplifier. The actuating force is directed into the first rod while the second rod is drive-coupled to the respective actuating device, e.g. an exhaust gas recirculating valve, to be actuated. With normal actuating resistance, for example with a non-sticking AGR-valve, the actuating forces can be directly transmitted from the first rod to the second rod via the compression spring, that is without force multiplication. With increased actuating resistance, e.g. with a sticking AGR-valve, the movement of the first rod results in the compression spring being compressed and, following an idle movement, in the actuation of the force amplifier, which via a toggle lever arrangement translates the large actuating travel of the first rod into a small actuating travel on the second rod, wherein a corresponding force amplification occurs at the same time. As soon as an initial sticking force has been overcome, the compression spring can again offset the remaining actuating travel.